(a) Field of the Invention
The present invention relates to a liquid crystal display and, in particular, to an optically compensated Birefringent mode liquid crystal display.
(b) Description of Related Art
Liquid crystal displays (LCDs) include two panels having pixel electrodes and a common electrode and a liquid crystal (LC) layer with dielectric anisotropy, which is interposed between the two panels. The pixel electrodes are arranged in a matrix, connected to switching elements such as thin film transistors (TFTs), and supplied with data voltages through the switching elements. The common electrode covers the entire surface of one of the two panels and is supplied with a common voltage. The pixel electrode, the common electrode, and the LC layer form a LC capacitor in circuital view, which is a basic element of a pixel along with the switching element connected thereto.
Among the LCDs, a twisted nematic (TN) mode LCD is usually used, but an optically compensated Birefringent (OCB) mode LCD has been developed and used for improving a response time of LC molecules and a view angle.
The OCB mode LCD uses a bend arrangement of the LC molecules and drives the liquid crystal with a voltage equal to or higher than a threshold voltage, which can maintain the bend arrangement.
The OCB mode LCD performs a preliminary operation of applying a voltage equal to the threshold voltage for obtaining a bend arrangement. The bend arrangement is obtained by shortly driving the TFTs with gate signals and data signals in the same way as the normal operation before starting main display operation. However, it is difficult to apply the exact voltage equal to the threshold voltage and the transition to the bend arrangement is too slow. Otherwise, the bend arrangement is obtained by applying a voltage generated by using a separate voltage generator such as a DC-to-DC converter. However, the addition of the separate voltage generator complicates the configuration of the LCD and limits the degree of freedom of the product design.